Modern medical imaging assemblies, such as x-ray tubes, are becoming increasingly powerful as their respective technologies advance. The increase in power and complexity introduces physical characteristics to the assemblies such as thermal growth that can effect the performance characteristics of the imaging assembly. Often these performance altering characteristics are related directly to increase power usage and may negatively impact image quality.
One such known effect of many x-ray tube assemblies is lateral drift of the focal spots. Under typical operating conditions, it is desirable for focal spot drift to be minimized. In addition, with the use of large and small focal spots in combination, it is often desirable for their drifts to be in opposite directions. Yet as cathode assemblies become more powerful and complex, the thermal properties in combination with the mechanical configurations make such drift control difficult. This is highly undesirably and can reduce the ability of the installation team to achieve a high level of image quality during tube calibrations.
One approach to minimizing focal spot drift would be through the development and introduction of active magnetic or electrostatic controls into the cathode assembly or directly onto the electron beam. However, such an approach would add undesirable cost increases to the system in addition to undesirable complexity. In addition, such complex solutions may be economically or structurally unfeasible for implementation onto existing imaging assemblies. Therefore, the use of magnetic control of the electron beam to steer and control the motion of the focal spots may be undesirable in many circumstances.
It would, therefore, be highly desirable to have an x-ray tube assembly that minimized the drift of focal spots without necessitating the introduction of complex and costly electronic or magnetic controls. It would additionally be highly desirable to have an x-ray tube assembly that harnessed the natural physical properties of existing tube structures to reduce the focal spot drift.